Foam inhibited oil



Nov. 18, 1947, v. N. BORSOFF ETAL FOAM INHIBITED OIL Filed July 14, 1942 2 Sheets-Sheet l M w w w 28km 1 SW ,5 082 200 250 Temperature Degrees Fahrenheit l N V E N TO RS V/cfar Al. Korsof'f' mes 0; flag/fan- Nov. 18,1947. vv. N. soRsoFF ETAL FOAM INHIBII'ED OIL Filed July 14, 1942 2 Sheets-Sheet 2 Duo m 0w 6 T Ln if r N.a 0 EN H Vwm A H Patented Nov. 18, 1947 2,430,858 roam mnmn'nn on.

Victor Borsoff and James 0. Clayton, Berkeley, Calif., asslgnors, by mesne assignments, to

California Research Corporation, San Francisco, 09111., a corporation of Delaware Application July 14, 1942, Serial No. 450,887

8 Claims. (Cl. 252-52) 1 This invention relates to oils inhibited against the formation of a stable bubble foam and to a method of inhibiting the foam formation tend-' ency of oils.

On mixing oil with air, a certain amount of foam may be created. The amount of foam will it pumps faster than required to pump all of the depend, among other things, upon the character 1 of the oil and the type of service in which it is employed. Thus most base mineral oils, that is mineral oils uncompounded with a chemical additive, do not readily form foam, at least under ordinary service conditions. Many compounded oils tend to produce a more stable foam than the base oils from which they are compounded. Thus petroleum lubricating oils compounded with metal naphthenates, higher metal alcoholates, higher metal alkyl phenates and metal salts of higher fatty acids foam more than the corresponding base oils. Many other additives cause more foam to be produced by oils to which they are added, than is formed by the base oils.

Oil foaming, even with compounded oils which display the greatest tendency to foam, is not always troublesome. Under conditions of little or no agitation, for example, trouble due to foaming is encountered, if at all, only in very exceptional cases. n the other hand, certain drastic types of service, involving extremely violent intermixture of oil and air or combustion gases, may produce an objectionable amount of foam with many oils. Between the extremes, however, of service causing little foaming of any oil and service causing much foaming of many oils, there are types of service and certain oils which, when used in combination, cause considerable difficulty. As stated, certain compounded oils exhibit a greater tendency to foam than the base oils, and when these compounded oils are used in certain types of lubrication systems, involving greater agitation of the oil and greater intermixture with gases than the ordinary crankcase lubrication of automobiles, the greatest practical difliculty is encountered.

Illustrative of the type oflubrication system which, when used with compounded lubricating oils having astrong tendency to foam, causes practical difliculty, is the dry sump lubrication system employed in many aircraft engines. In this system, oil from the moving parts of the motor is collected in the crankcase and pumped from there to an external tank or sump by a scavengingpump. Oil from this sump is pumped back to the motor in the usual manner by an oil pump. The foaming difiiculty arises from the-fact that the scavenging pump operates at excess capacity available oil in the crankcase. It therefore pumps a great deal of air along with the oil, and this at a rapid rate, and the result in entrainment of air in the oil and the formation of foam. As a consequence, excessive foaming occurs when oils such as the aforementioned compounded oils are used and oil is lost through the breather pipes, lnsufficient lubrication results because of the presence of air in the oil supplied to the motor, and other disadvantages result.

011 also forms a more persistent foam if it contains water (as in solution) and is then heated and suddenly subjected to a, verylow pressure, as; for instance, in an airplane engine climbing from a'low altitude to 40,000 feet at a high speed.

In other instances, as in the lubrication of gears with heavy oils, foaming ditlicultles may also be encountered.

It is an object achieved by the present invention to inhibit the foaming of oils.

It is a further object achieved by th present invention to inhibit the foaming of compounded mineral lubricating oils. 4

, It is a still further and a particular object achieved by the present invention to obviate the problem of excessive foaming of compounded mineral lubricating oils when used in types of lubrication service involving severe conditions of intermixture of oil and gases..

Other objects achieved by the invention will be apparent from the following description and from the claims.

We have discovered that foaming of oils can be inhibited by incorporating therein a small amount of an aliphatic compound containing not less than about 25 per cent by weight of oxygen and preferably containing a plurality of groups selected from the class consisting of hydroxyl, carbonyl, alkoxy, cycloalkoxy and oxime groups.

We have found that such oxygen-containing aliphatic compounds are efiective in reducing foaming evenwhen used in very small amounts, and that they are most effective in inhibiting the foaming of compounded lubricating oils. They are, however, not limited in their effectiveness to compounded oils but may be used to advantage in dealing with a variety of foaming problems. Certain of the foam inhibitors falling within the designated class are more effective than others for a given set of conditions, whereas for another set of conditions a different group of inhibitors will be found to be superior.

The class of inhibitors falling within the scope 3 4 of the present invention will first be illustrated with reference to the oxygen-containing part of the molecule and then with reference to speciflc Dimethyl ether Acetal examples of inhibitors. The oxygen may be pres- Methyl ethyl ether Carbltol ent in any form but preferably it is present in the 6 E hylene oxide Methyl carbitol form of hydroxyl, carbonyl, alkoxy, cycloalkoxy Allylene oxide Butyl carbitol or oxime groups. The hydroxyl group may be y tol anhydride Cellosolve present in the form of alcoholic hydroxyl, for ex- Methyl furiuryl ether Methyl cellosolve ample in the form of a polyhydric alcohol, an hy- Glycerine allyl ether Butyl cellosolve droxy carboxylic acid or an hydroxy 'carboxylic l ester. The hydroxyl radical may, however, be a Esrlas more acidic hydroxyl, as in the case oi. the OH of l a carboxylic acid, or it may be present in the form Methyl formate Ethyl crotonate of an NOH group, as in the oximes. Two or Methyl glyoxyla'te Ethyl metmrylate more types of hydroxyl group may be present in fi i y oxalate A1171 Propmnate the same molecule. yl acrylate Ethyl momma The carbonyl group may be present in such 3 gg t plmpmmtg forms as carboxyllc acid or ester, ketone, or aldey a e acrylate Hyde groupings, onloefhyl oxalate Ethyl acetoacetate The alkoxy and cycloalkoxy groups may be fi z dikztttbutyl'ate Pyl Dyruvate lresent in such forms as carbomlic ester groups 5 ace e Dimethyl succmg'te and ethers. a. g g i fir The oxygen-containing groups of an inhibitor 8 Y on a 9 may all be of the same type, e. g., ketonegroups, g2??? kftonalonate methyl malate or they may be of mixed types, such as alcoholic 5 e lfimethyl tartmte and carboxylic hydroxyls, or ketone and alcoholic A1 e ethyl butymte hydroxyl groups. aceta e Ethyl butymte The inhibitors of our invention include the cyfi acetoi'cetat-e Methyl Valera-t8 clic aliphatic compounds, such as dioxane, cyclo- 3 'g f m t Butyl acetate pentane dicl, cyclohexane triol, p-menthane triol, M th i a e Amyl format! p-menthene triol, cyclobutane dlone, cyclohexg 31: e t Ethyl hydmxybutymte ane dione and cyclohexanol-(2) son-(1), which g z e Egg} it zz ntaln at least about 25 er cent b we! ht gi p y g of 3: 1: 3 Mi -g Diethyl malonate Specific examples typlfylng the class oi inhibacry 8 methyl mala'te itors which we have found to be efiectlve are the gi carbitol acetate following: t eats M m For Cent Inhibitor Molecular Structure g gygggllg Pro ylene glycol CHl-CH OHLCHgOH 76 42.0 2,3l l utylcne glycolcmononycmomcn.-- 35.6 Propicnyl acetone C;HsCO.CH:.CO.CHi 114 28.0

Dlznethyl glyoxine GH.C=NOH 115 27.6

cm. =NOH Ethyl mammalian" cmcocmcoocsm 37.0

Ethyl oxalate COOGQH 146 43.8

OOCsHu Trlethauolamino (H0 CH!.CH:)aN 149 32.2

assfzifiniwlrther examples of foam inhibitors are Ammms mm mm Formaldehyde Diacetyl MONOHYDRIC ALCOHOLS Paraformaldehyde Acetone M y a1 0 An 1 1 h 1 60 getene Acetoacetaldehyde e Y c0 0 y xal Succinalde de Ethyl alcohol Propargyl alcohol Acetaldehyde F'lu'fulal by rowl alcohol Furfuryl alcohol Propargyl aldehyde Acetyl acetone Iso-propyl alcohol Diacetone alcohol Mesoxaldehyde Ievulinaldehyde a5 Acrolein Methyl allyl diketone POLYmRIc ALOOHOI-B Methyl glyoxal Acetonyl acetone Propylene glycol Hexene diols i fzigj Dlpromonyl Trimethylene glycol Butine diols Butane diols Pentlne diols 7o ma neto am ce :0 y e Hexane diols Heptane triols Butene diols Octane trlols Pentene dlols Nonane triols 75 Butyrolactone Valerolactone Acetyl acetic acid Caproic acid Preferably we use as foam inhibitors oxygencontaining aliphatic compounds containing not less than about 25 per cent by weight of oxygen,

' and having a molecular weight not higher than about 225. We also prefer to use as inhibitors those compounds which' are soluble in mineral oil to the extent used. Less soluble inhibitorsare more likely to be removed by filtration or to settle out on standing. However, oil solubility is not essential to effectiveness in reducing foam and a solubility on the order of 0.001 per cent by weight based on the oil is adequate.

The inhibitors of our invention may be advantageously used in a wide variety of oils, including naphthenic base, paraflin base and mixed base mineral oils, in synthetic oils, and in oils of viscosity ranging from 40 SSU or lower at 210 F. to 150 SSU or higher at 210 F.

Preferably the foam inhibitors of the present invention are used in the finished oil in an amount equal to about 0.001 to 1 per cent by weight based on the oil. If the oil is a compounded oil containing 0.1 to 5 per cent by weight of an additive which promotes foaming, the foam inhibitor is preferably used in an amount equal to about to 200 per cent by weight based on the additive.

Concentrated solutions of foam inhibitor in oil may be prepared. Such concentrates may also contain other compounding agents. By diluting the concentrate with more oil, a finished oil can be produced containing foam inhibitor, or foam inhibitor and other compounding agent or agents in the desired amount. Conveniently, concentrates containing from about 1.0 to per cent by weight of foam inhibitor based on the total concentrate are thus prepared, in cases where the foam inhibitor is suificiently oil soluble.

The following specific examples will serve to illustrate the advantages and effectiveness of the inhibitors of the invention in reducing foam formation Example I.--The foaming qualities of various oils were observed. The base stock was a solvent treated, paramnic base oil having a viscosity of 120 SSU at 210 F., and a viscosity index of 86. The first oil tested consisted of this base stock alone and the second oil consisted of. the

base stock compounded with 0.25 per cent by weight of a 2:1 mixture 'of calcium alkyl phenate and calcium cetyl phosphate. The calcium alkyl phenate so used was the salt of an alkyl substituted phenol prepared by condensing butene polymers, having an average molecular weight of about 196, with phenol. The calcium cetyl phosphate so used was the salt prepared from a mixture of monocetyland dicetyl-phosphoric acids. The remaining oils each consisted of base stock,

0.25 per cent by weight of the same phenate- I phosphate mixture, and 0.1 per cent by weight of a foam inhibitor. The test conditions were as follows:

500 cc. of the oil were placed in a cylindrical 6 metal container 6 inches in diameter by 5 inches high and a Mix-Master" stirrer of the type used in household kitchens was lowered into the oil..

The oil was slowly heated by means'of an electric'hot plate and the amount of foam produced was measured at various temperatures up to 300 F. The speed of the stirrer was 1100 revolutions per minute. The test results at 275 F., under identical operating conditions except for variation of the oil composition, are set forth in Table I below:

" Table I Per cent increase in volume Uncompounded oil 11 Compounded oil 57 The per cent increase in volume referred to in the above table, and again in Table II below, is arrived at by observing the increase in volume of the mixture of foam and oil over the original volume of oil, dividing the increase by the original volume of oil, and multiplying by 100. It is, therefore, the volume of foam produced reckoned as per cent of the original volume of oil.

Example Il.Oils were tested in an apparatus comprising a reservoir adapted to be heated by a hot plate, a sump situated below the reservoir, a, drain provided with a regulating valve and leading from the bottom of the reservoir to the sump, and a return conduit connected with the bottom of the sump, provided with a pump, and extending into, the reservoir under the surface of the oil therein. Oil, maintained at 200 F. in the reservoir, dropped from the reservoir through the drain to the sump at a rate controlled by the regulating valve. duit was operated at a capacity three times the rate of flow of oil into the sump; therefore, both oil and air were pumped from the sump to the reservoir and foaming was caused in the reservoir. At the end of each 30 minutes of operation, the volume of foam and oil in the reservoir was observed. The amount of foam was calculated as the per cent increase in volume over the original volume of oil. Under identical operating conditions, various oils produced increase in volume as given in Table-II below:

Example [IL-A 1939 Ford V-8, horsepower engine was thus modified: The bottom of the crankcase was connected to a, large glass container and the suction line of the oil pump was connected to the glass container. Oil dropping from the moving parts drained from the crankcase through the pipe to the glass container and was pumped back to the engine from the glass container through the suction line. The air pressure in the crankcase was maintained at 1% inches of mercury. In this manner air became The pump in the return contemperatures.

' Depth of foam in inches compounded oil A 1 compounded oil'A+0.1% ethyl tartrate 0.13 compounded oil B 3.5 compounded oil B+0.1% propylene glycol" 0.19

compounded oil A was a solvent treated, parafflnic base oil hating a viscosity of 120 SSU at 210 F. and a viscosity index of 86. The compounding agent was 0.5 per cent of a calcium alkyl phenate. Compounded oil B was the same base 011 compounded was 0.25% of a 2:1 mixture of calcium alkyl phenate and calcium cetyl phosphate.

As stated above, the inhibitors of the invention are not all equally effective in inhibiting foam formation. Some of theinhibitors are less eflective than others under all or most conditions. Some inhibitors are the most effective under certain conditions, whereas others are the most effective under other conditions. Thus, as shown by the above specific examples, triethanolamine is among the most highly effective inhibitors both in the open vessel-mechanical stirrer test (Example I) and in the sump test (Example 11) 2,3-butylene glycol, on the other hand, although eflecting a very substantial reduction of foaming in both these tests, is among the least effective of the inhibitors tested, judged by either test. Propylene glycol illustrates the'polnt that a given inhibitor may give better performance under one set of conditions and poorer, though substantial results under another set of conditions. Thus, propylene glycol was one of the least effective inhibitors under the conditions of the open vesselmechanical mixer test, but it was the most efiective inhibitor in the sump test.

We have observed that our inhibitors are more eflectiveat elevated temperatures than at lower At about the ordinary temperature, the reduction in foaming produced by the inhibitors of the invention is small, although substantial. At about 120 to 150 F. the reduction of foaming begins to be large, and above about 150 F. the reduction in foaming is very large.

The effect of temperature upon foaming of unthan that of oil B. At about 190 F., however,

oil B began to foam more with increase in temperature, whereas oils A andC continued to. foam to about the same degree.

It will be noted that the inhibitor exerted greater effectiveness in reducing foam formation at higher temperatures than at lower temperatures. From the standpoint of foam formation in internal combustion engines this is important. crankcase temperatures are generally above about 200 F., although the crankcases of some engines operate at temperatures as low as about 150 F. It is at temperatures above about 150 F., especially above about 200 F., that excessive foaming is likely to occur. At these temperatures the inhibitors of our invention are highly eflective in reducing foam formation.

The phenate-phosphate mixture referred to above is effective in inhibiting oxidation of lubricating oils and in reducing ring sticking. It is given by way of example of the oil-soluble metal organic salts which are widely used in lubricating oils for such purposes. The tendency of such compounding agents to promote foaming detracts somewhat from their utility, and the obviation of this defect, by the use of our foam inhibitors, is

I one of the principal objects accomplished by the inhibited and inhibited oils is shown by Fig. 1 of acetoacetate. The test conditions were the same as in Example I, except that observations were made-at a. number'of different temperatures.

It will be noted that foaming was great in the case of all three oils at about 100 F., though less with oil A (uncompounded oil) and oil C (compounded oil containing ethyl acetoacetate) than with oil B (compounded oil containing no ethyl acetoacetate) As the temperature increased, the foaming of all three oils decreased, but the foaming of oils A and 0 decreased more rapidly invention.

It has been found that .certain compounded oils which foam excessively also develop surfaces having the characteristics of plastic solids; that is, the surface is highly viscous, yields to and is deformed by a pressure in excess of a minimum yield value, but does not flow freely like a liquid under the force of gravity. This fact has been brought to light through the use of the torsion pendulum. This apparatus and its use todetermine surface plasticity and viscosity of aqueous solutions is described-by R E. Wilson and E. D. Ries in Surface films as plastic solids," Colloid Symposium Monograph, volume I, pages -173, published by the Department of Chemistry, University of Wisconsin, 1923. The same apparatus and method were used to determine ing oil and the compounded oil exhibits a marked tendency to foam under the conditions of Example I. It was found that at room temperature the surface of the compounded oil,'on ageing, be came very viscous and similar to a plastic solid. However, when 0.1% of ethyl acetoacetate was dissolved in the compounded oil, a similar viscosity increase occurred on ageing following which a slow decrease in surface viscosity set in and upon continued standing the surface became thixotropic; could even be made liquid by rotation of the torsion pendulum. A similar phenomenon occurs at more elevated temperatures, such as 200 F.

Thus there is a correlation between surface viscosity and foaming tendency; the excessively foaming eil formed a surface, on ageing, similar to a plastic solid, but the foam inhibited oil formed a liquid surface or a plastic solid surface of very low yield point.

Therefore, those oils whose surfaces on ageing (a matter of minutes) exhibit the properties of plastic solids with high yield points are ex- 9 cessively foaming oils, while oils whose surfaces on ageing remain liquid or exhibit the properties of plastic solids with very low yield points are not excessively'foaming oils. The most probable explanation of these observed phenomena. seems to be as follows: All oils, when agitated with air produce foam, which consists of small portions of air each surrounded by a film of oil. In many cases this foam is unstable, probably due to the instability of the film of oil. This film is so fluid that continued agitation and collisions of the foam bubbles witheach other and the sides of the vessel and draining of the liquid from the film cause rupture of the film and destruction of the bubbles. In those cases, however, where the oil surface (hence the film of oil enclosing the air in the foam) is a plastic solid, the film is not as easily ruptured because the liquid cannot drain from the film due to capillary forces set up by the plastic solid surfaces, and the foam is stable. The plasticity and stability of the oil film clearly depend, in part at least, upon the nature and amount of solutes in the oil. Thus metal salts such as metal naphthenates, metal s ps of higher fatty acids, higher metal alkyl phenates, metal salts of phosphoric acid partly esterifiied by long chain alcohols, and higher metal alcoholates are apparently adsorbed by the film of oil and render it more viscous, plastic and tough. We do not wish to infer that this is the only factor influencing foaming or that all foaming is due to the formation of a plastio'solid film,

but this is one of the principal contributing factors. The inhibitors of this invention, such as ethyl acetoacetate, apparently function by reducing the amount of adsorption of the foamproducing salts in the film, or are themselves adsonbed and counteract the adsorbed foam-producing salts.

Our invention, however, is not limited in its application to those oils which, because of certain salt-like compounding agents, form viscous, plastic surfaces. Our invention is applicable broadly to the inhibition of oil foaming wherever it occurs and comprises the addition of our foam inhibiting agents to any oil which foams excessively.

For the purpose of clarity, the terms excessive foaming, excessively foaming, and the like, as applied to oils herein and in the claims, refer to performance under the conditions of the following reproducible test, described with reference to Figs. 2 and 3 of the accompanying drawings. An oil which, when agitated under the conditi of this test at 275 F., increases in .volume d 'riginal volume, is an "excessively foaming oil, and oils which foam less than this amount are not "excessively foaming" oils.

500 cc. of oil are placed in a cylindrical fiat bottomed container 6" in diameter and high (intemal dimensions), the oilin the container isbrought to and maintained at 275 F. by any suitable means such as a hot plate or a jacket,

I and the stirring elements of a Mix Master stirrer of the type used in household kitchens is lowered into the container. The Mix Master" stirrer is the product of and obtainable from the Chicago Flexible Shaft 00., 1124 South Central Avenue, Chicago, Illinois. The stirring elements are similar in construction and action to the familiar househpld'egg beater, consisting of two shafts oppositely rotated by a motor, and two elliptical loops attached to each shaft, one loop being at right a lel s to the other and the two e tofoaming by more than 20 per cent of its loops having [a common long axis; The dimensions and form of the vessel and" stirring elements will be better understood, and can be duplicated by, reference to Figs. 2 and Fig. 2 shows, partly in cross section and partly in front elevation, the container and the stirring elements, while Fig. 3 shows in front elevation a detailed view of one-half of one loop of one stirring element.

Referring to Fig. 2, the apparatus comprises a cylindrical flat bottomed container I and two stirring elements If constructed exactly alike. The internal-dimensions of the container, as shown, are a diameter of 6"and a height of 5". The tirringelements consist each of an upper shaft A geared at the top to a motor (not shown) and rigidly secured at the bottom to a lower shaft 3 and to two elliptical loops 0 and D which are disposed at right angles to each other and have 'each the shaft B as their long axis and as a supporting member. Shaft B is rigidly secured to the tops and bottoms of loops C and D. In the preferred construction, as shown, shaft A is sturdier than shaft B, but this is not necessary; for example, a single shaft of uniform diameter may take the place 'of shafts A-and B, passing through the tops of loops 0 and D and being secured thereto at the top and bottom 'of the loops. The stirring elements II are so placed in vessel I that shafts A are parallel and 1%" apart (center to center) and they are placed in vessel I so that a hne drawn half way between and in the plane of the shafts coincides with the axis of vessel I, and the distance from the bottom of loops 0 to the bottom of vessel I is 54, inch. The shafts A are so geared to the motor that they rotate at equal speeds and in opposite directions.

Referring to Fig. 3, shafts A and B and one-half of loop C are shown. The other half of loop 0, and both halves of loop D are identically constructed.

Shaft B is cylindrical and has a diameter of Mr" and a length of 3%". Loop Cconsists of a flat strip of metal or equivalent material 5 thick and 34 wide. It is bent approximately in the shape of an ellipse with a short radius of 1%". It has fiat sides 1%" long, and the portions between the fiat sides and shaft B have approximately the curvature of a circle.

Small variations of the structure of the loop and of the diameter of shaft 13 may be made without altering substantially the results obtained.

In operation. the oil container I is maintained at 275 F.'and stirring elements A are rotated in opposite directions each at the rate of 1100 revolutions per minute. The volume increase due to foaming is determined by measuring the height of the oil before foam formation and after foam formation.

We claim".

1. A compounded hydrocarbon lubricating oil comprising a major proportion of the hydrocarbon oil of lubricating viscosity, 9. small amount of a, metal salt selected from the group consisting of oil-soluble metal salts of organic acids and oilsoluble metal salts of organo-substituted inorganic acids, said salt being present in amount sufficient to increase substantially the tendency of the oil to foam when subjected to agitation with 11 molecule and containing not less than about 25% i by weight oi oxygen.

3. The compounded oil oi claim 1. wherein said metal salt is an oil-soluble polyvalent metal salt oi an, organorsubstitute'd acid 01 phosphorus.

4. The compounded oil 01 claim 1, wherein said aliphatic compound contains a plurality of groups selected from the class consisting of hydroxyl, carbonyl, alkoxy, cycloalkoxy and oxime groups.

5. The compounded oil 01 claim 1, wherein said aliphatic compound is ethyl acetoacetate.

6. The compounded oil of claim 1, wherein said aliphatic compound is propylene glycol.

7. The compounded oil of claim 1, wherein said aliphatic compound is dimethyl glyoxime.

8. A compounded petroleum lubricating 011 comprising a major proportion of petroleum oil oi lubricating viscosity, a small amount or an Oilsoluble polyval'ent metal salt of a phenol and a small amount of an oil-soluble polyvalent metal salt of an organo-substituted acid of phosphorus, said metal salt of a phenol and said metal salt 01' an acid of phosphorus being present in amount sumcient to increase substantially the tendency of the oil to foam when subjected to agitation with air, and about 0.001 to 1 percent by weight, suiflcient substantially to inhibit foaming oi the oil when subjected to agitation with air, of an allphatic compound consisting of elements selected from the group consisting of carbon, hydrogen, oiwgen and nitrogen, having a molecular weight 12 not greater than about 225, containing at least two oxygen atoms in the molecule and containin not less than 25% by weight 01' oxygen. VICTOR N. BORSOFF.

JAMES O. CLAYTON.

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